The present invention relates to a process for determining the weight of free-falling molten glass gobs.
Modern glass vessel production machines process up to 200 gobs of glass per minute, which are delivered to the machines from the melt via a feeder system. An approximately constant weight of the glass gobs produced by a metering device is essential, since fluctuations in weight lead to articles of poorer quality or even to rejects. Even with a properly functioning metering device, however, fluctuations in weight cannot be avoided since the metering process is affected, among other factors, by the level of the glass melt in the melting tub and/or by temperature fluctuations of the melt. These fluctuations can amount to several grams per minute.
To keep the weights of the glass gobs within the allowable range, in a method known from the prior art the finished glass articles are weighed continuously at intervals of 5 to 15 minutes. Following each measurement, the metering device is then adjusted manually--if necessary. The weighed articles have to be thrown away after weighing, since they are damaged by being manipulated while still cooling down.
To automate this process, U.S. Pat. No. 3,846,107 proposes carrying out the weighing with electromechanical scales and supplying the ascertained weight to a controller as a measurement variable. By a comparison of set-point and actual values, an appropriate adjustment of the metering device is then done via the controller. This method allows determining the weight at the earliest after the article has been taken from the finished form, but usually not until much much later. This involves major mechanical effort and expense; the mechanism is vulnerable to malfunction and is subject to continuous wear. Moreover, in both this and the method described above, any reaction to fluctuations in weight occur only after a not-inconsiderable time lag.
This disadvantage is averted with the method of U.S. Pat. No. 4,205,973. Here, among other parameters, the volume and hence the weight of molten glass gobs free-falling in the feeder system of a glass container production line are determined. To that end, two line-scanning cameras are used, which detect the volume of the dropping glass gob slice by slice. Once all the data of one glass gob are available, its volume or weight is calculated via a computer.
In this method, the weight of the glass gobs produced is already determined early by comparison with the methods described earlier herein, so that better regulation of the metering device is possible. This advantage is bought at the cost of very major technological effort. Moreover, the cameras required are not especially well suited to the severe conditions of the glass melt, and hence much effort has to be expended for maintaining and caring for them.
German Published, Examined Patent Application DE-AS 19 59 406 describes a measurement probe operating by the eddy current principle. In one application, two of these measurement probes act as a weighing device. The weight of the specimen changes the spacing between the measurement probes and highly conductive slices associated with and located opposite them. In the measurement probe, this generates eddy current losses, which are proportional to this change in spacing and represent a standard for the weight of the specimen. Thus the probes function as distance meters.